Question

Chromatographic features comparison: Predict the relative Rf values for the pigments, lycopene and B-carotene, on a TLC plate. Which pigment will elute firsr during column chromatography? explain in detail.

Answer 1

When we perform TLC, the mobile phase moves up via capillary action. Separation occurs when one component of the mixture is strongly adsorbed by the stationary phase than the other component.. The Rf value is a way to express the position of a substance on a developed chromatogram.

As beta carotene is less polar which makes it more soluble in the TLC solvent (hexane, non or less polar) and adsorbing less to the stationary phase than lycopene which is more polar. Hence,beta carotene carries the highest Rf value than lycopene.

Adsorptivity of compounds increases with increased polarity which in turns yield lower Rf values on TLC.

In column Chromatographybeta carotene will elute first being its less polar nature because it has less double bonds than lycopene. More polar Lycopene sticks to the column more readily than beta carotene, and therefore takes longer to move down. (beta- carotene contains less number of conjugated double bonds)

HA HzC CH3 CHE sa CH CHz HC CHg Trans Beta Carotene

H3CO CH3 CH3 Lycopene